Patent GB-668164-A (GB)
Title: Electrical measuring device in which variable currents or voltages are converted into characteristic pulse trains
IPC: G08C19/22
Filed: 1948-02-27
Abstract: 668,164. Current and voltage measuring apparatus. STANDARD TELEPHONES & CABLES, Ltd. Feb. 27, 1948 [Feb. 27, 1947], No. 6076/48. Class 37. [Also in Group XL (c)] An electrical measuring device, for measuring the magnitude of a D.C. voltage from a source 5 (Fig. 1), comprises a polarized relay comparator 1, having three windings 2, 3, 4, the winding 2 being in opposition to the winding 4 and fed from the source 5. The winding 4 is coupled, through a time constant circuit comprising resistors 6 and 7 and condenser 8 to a constant source of D.C. energy 10. The winding 3 is connected to a positive supply either through resistance 14 or potentiometer 11, the current flow therethrough being reversible by means of relay contacts 12. In operation, as soon as current flows through winding 2, current also flowing in the opposite direction from resistance 14 through winding 3 to the earthy side of potentiometer 11, the relay is energized to close contact 12, thereby reversing the current flow through winding 3 and energizing a relay 13 to close contacts 9 and 15. Closure of the contact 9 applies energy to the winding 4 and condenser 8 so that as soon as the charge on condenser 8 is built up to a value such that the effect of the winding 4 overcomes that of windings 2 and 3 the relay is de-energized. Assuming V (Fig. 2) to be the voltage of the source 5, the condenser voltage rises along the charging curve 26 to a point 28 when the relay is de-energized. Contact 12 is thus opened, reversing the current flow through winding 3 and de-energizing relay 13 to open contacts 9 and 15. The constant source 10 is now disconnected from the condenser 8 which begins to discharge through resistance 6 along a curve corresponding to its discharge curve 29 until the combined effects of the windings 3 and 4 are insufficient to overcome the effect of the winding 2 when the relay 1 again becomes energized, i.e. at point 30 (Fig. 2). Contacts 15 of the relay 13, being closed when the condenser 8 is charging, serve to energize a relay 19 to connect a source 23 to a wattmeter 25 or other suitable device for integrating the pulses of current 32, 33 so produced, thus giving a measure of the value of the source 5. Should the value of that source vary, e.g. to a value V<SP>1</SP> (Fig. 2), since the condenser 8 is charged and discharged on different parts of its characteristic curves, the times of charge and discharge are varied and the width of the current pulses 35 to be integrated varies in proportion to the variation from V to V<SP>1</SP>. The apparatus may be used to measure slowly fluctuating D.C. voltages. In a modification, Fig. 3 (not shown), the variable D.C. source is applied to an amplifier before being applied to the winding 2. In this embodiment also both the voltage across the condenser due to the constant D.C. source and the voltage due to the variable source operate on winding 2, the winding 4 having applied thereto a constant voltage such that the ampere turns in winding 4 balance the ampere turns in winding 2 when the variable source 5 is zero.